Method of making self-doped zwitterionic heterocyclic polymers

ABSTRACT

A self-doped conducting polymer having along its backbone a π-electron conjugated system which comprises a plurality of monomer units, between about 0.01 and 100 mole % of the units having covalently linked thereto at least one Bronsted acid group. The conductive zwitterionic polymer is also provided. as are monomers useful in the preparation of the polymer and electrodes comprising the polymer.

This is a divisional of copending applications, application Ser. No.08/336,328, filed Nov. 8, 1994, which is a continuation of applicationSer. No. 08/016,658, filed on Feb. 9, 1993, now abandoned, which is acontinuation of U.S. application Ser. No. 07/607,851, filed on Nov. 1,1990, now abandoned, which is a continuation of U.S. Ser. No.07/156,928, filed Dec. 14, 1987, now abandoned, which claims priority onInternational application PCT/US86/02042, filed on Sep. 29, 1986, whichclaims priority on Japanese patent application 64272/86, filed on Mar.24, 1986.

FIELD OF THE INVENTION

This invention relates generally to the field of conducting polymers.More particularly the invention relates to self-doped conjugatedpolymers in which Bronsted acid groups are covalently bound to thebackbone of the polymer.

BACKGROUND

The requirements for conductive polymers used in the electronic andother industries are becoming more and more stringent. There is also anincreasing need for materials which permit reduction in the size andweight of electronic parts and which themselves exhibit long-termstability and superior performance.

In order to satisfy these demands, active efforts have been made inrecent years to develop new conductive macromolecular or polymericmaterials. A number of proposals have also been made regarding thepotential uses of such new compounds. For example. P. J. Nigrey et al.in Chem. Comm. pp. 591 et seq. (1979) have disclosed the use ofpolyacetylenes as secondary battery electrodes. Similarly, in the J.Electro Chem. Soc., p. (1981) et seq. (1651) and in Japanese PatentApplication Nos. 136469/1981, 121168/1981, 3870/1984, 3872/1984,3873/1984, 196566/1984, 196573/1984, 203368/1984, and 203369/1984, havealso disclosed the use of polyacetylenes, Schiff base-containingquinazone polymers, polarylene quinones, poly-p-phenylenes,poly-2,5-thienylenes and other polymeric materials as electrodematerials for secondary batteries.

The use of polymeric materials in electrochromic applications has alsobeen suggested, in, e.g., A. F. Diaz et al., J. Electroanal. Chem. 111:111 et seq. (1980). Yoneyama et al., J. Electroanal. Chem. 161, p.419(1984) (polyaniline), A. F. Diaz et al., J. Electroanal. Chem. 149:101 (1983) (polypyrrole). M. A. Druy et al., Journal de Physique 44:C3-595 (June 1983). and Kaneto et al., Japan Journal of Applied Physics22(7): L412 (1983) (polythiophene).

These highly conductive polymers known in the art are typically renderedconductive through the process of doping with acceptors or donors. Inacceptor doping, the backbone of the acceptor-doped polymer is oxidized,thereby introducing positive charges into the polymer chain. Similarly,in donor doping, the polymer is reduced, so that negative charges areintroduced into the polymer chain. It is these mobile positive ornegative charges which are externally introduced into the polymer chainsthat are responsible for the electrical conductivity of the dopedpolymers. In addition, such "p-type" (oxidation) or "n-type" (reduction)doping is responsible for substantially all the changes in electronicstructure which occur after doping, including, for example, changes inthe optical and infrared absorption spectra.

Thus, in all previous methods of doping the counterions are derived froman external acceptor or donor functionality. During electrochemicalcycling between neutral and ionic states. then, the counterions mustmigrate in and out of the bulk of the polymer. This solid statediffusion of externally introduced counterions is often therate-limiting step in the cycling process. It is thus desirable toovercome this limitation and thereby decrease the response time inelectrochemical or electrochromic doping and undoping operations. It hasbeen found that the response time can be shortened if the periodrequired for migration of counterions can be curtailed. The presentinvention is predicated upon this discovery.

SUMMARY OF THE INVENTION

The present invention provides conducting polymers that can be rapidlydoped and undoped, and which are capable of maintaining a stable, dopedstate for long periods of time relative to conducting polymers of theprior art. The superior properties of the polymers of the presentinvention result from the discovery that conducting polmers can be madein a "self-doped" form: i.e., the counterion that provides conductivitycan be covalently linked to the polymer itself. In contrast to thepolymers of the prior art, therefore, the need for externally introducedcounterions is obviated, and the rate-limiting diffusion step alluded toabove is eliminated as well.

The polymers of the invention can display conductivities of on the orderof at least about 1 S/cm. The self-doped polymers may be used aselectrodes in electrochemical cells, as conductive layers inelectrochromic displays, field effective transistors. Schottky diodesand the like, or in any number of applications where a highly conductivepolymer which exhibits rapid doping kinetics is desirable.

In its broadest aspect, the present invention is directed to aconducting self-doped polymer having along its backbone a π-electronconjugated system which comprises a plurality of monomer units, betweenabout 0.01 and 100 mole % of said units having covalently linked theretoat least one Bronsted acid group. The present invention also encompassesthe zwitterionic form of such polymers. Polymers which may form thebackbone of the compounds of the present invention include, for example,polypyrrole, polythiophenes, polyisothianaphthenes polyanilines,poly-p-phenylenes and copolymers thereof.

In a preferred embodiment, self-doped polymers described above have arecurring structure selected from the following structures (I) or (II):##STR1## wherein, in Formula I: Ht is a heterogroup: Y₁ is selected fromthe group consisting of hydrogen and --R₁ --X--M₁ ; M₁ is an atom orgroup which when oxidized yields a positive monovalent counterion; X isa Bronsted acid anion: and R₁ is a linear or branched alkylene, ether,ester or amide moiety having between 1 and about 10 carbon atoms. InFormula II, Y₂, Y₃ and Y₄ are independently selected from the groupconsisting of hydrogen and --R₂ --X--M₂, R₂ is a direct bond, a linearor branched alkylene, ether, ester or amide moiety having between 1 andabout 10 carbon atoms, and M₂ is an atom or group which when oxidizedyields a positive monovalent counterion.

In yet another preferred embodiment of the invention, a conductivepolymer is provided containing a recurring zwitterionic structureaccording to (Ia) or (IIa): ##STR2## wherein Ht, R₁, R₂ and X are asdefined above.

The invention is also directed to monomers useful in making the aboveself-doped polymers, methods of synthesizing the polymers, and devicesemploying the polymers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an infrared spectrum ofpoly(methylthiophene-3-(2-ethanesulfonate)):

FIG. 2 is an infrared spectrum of poly(thiophene-3-(2-ethanesulfonicacid sodium salt)):

FIG. 3 is an infrared spectrum of poly(methylthiophene-3-(4-butanesulfonate)):

FIG. 4 is an infrared spectrum of poly(thiophene-3-(4-butanesulfonicacid sodium salt)):

FIG. 5 depicts a series of vis-near ir spectra ofpoly(thiophene-3-(2-ethanesulfonic acid sodium salt)):

FIG. 6 depicts a series of vis-near ir spectra ofpoly(thiophene-3-(4-butanesulfonic acid sodium salt)):

FIG. 7 depicts a series of vis-near ir spectra ofpoly(methylthiophene-3-(4-butane sulfonate)):

FIG. 8 illustrates the results of cyclic voltammetry carried out onfilms of poly(thiophene-3-(2-ethanesulfonic acid)); and

FIG. 9 depicts a series of vis-near ir spectra ofpoly(thiophene-3-(2-ethanesulfonic acid).

DETAILED DESCRIPTION

The terms "conducting" or "conductive", indicate the ability to transmitelectric charge by the passage of ionized atoms or electrons."Conducting" or "conductive" compounds include compounds which embody orincorporate mobile ions or electrons as well as compounds which may beoxidized so as to embody or incorporate mobile ions or electrons.

The term "self-doping" means that a material may be rendered conductingor conductive without external introduction of ions by conventionaldoping techniques. In the self-doping polymers disclosed herein,potential counterions are covalently bound to the polymer backbone.

The term "Bronsted acid" is used to refer to a chemical species whichcan act as a source of one or more protons. i.e. as a proton-donor. See.e.q., the McGraw-Hill Dictionary of Scientific and Technical Terms (3rdEd. 1984) at page 220. Examples of Bronsted acids thus includecarboxylic, sulfonic and phosphoric acids.

The term "Bronsted acid group" as used herein means Bronsted acids asdefined above, anions of Bronsted acids (i.e. where the protons havebeen removed), and salts of Bronsted acids, in which a Bronsted acidanion is associated with a monovalent cationic counterion.

"Monomer units" as used herein refer to the recurring structural unitsof a polymer. The individual monomer units of a particular polymer maybe identical, as in a homopolymer, or different, as in a copolymer.

The polymers of the present invention, which may be copolymers orhomopolymers, have a backbone structure that provides a π-electronconjugated system. Examples of such polymer backbones include, but arenot limited to, polypyrroles, polythiophenes, polyisothianaphthenes,polyanilines, poly-p-phenylenes and copolymers thereof. The recurringstructure described above may constitute anywhere from about 0.01 toabout 100 mole % monomers substituted with one or more --R₁ --X--M₁ orR₂ --X--M₂ functionalities. In applications requiring high conductivity,usually at least about 10 mole % of the monomer units are substituted,typically about 50 to 100 mole %. In semiconductor applications, it isusually less than about 10 mole % of the monomer units that aresubstituted, sometimes as little as about 0.1 or about 0.01 mole %.

Polyheterocycle monomer units represented by Formulae I and Ia includemonomer units which are either mono-substituted or di-substituted withthe --R₁ --X--M₁ functionality. Similarly, the polyaniline monomer unitsrepresented by Formulae II and IIa include monomer units which aresubstituted with 1, 2, 3 or 4 --R₂ --X--M₂ substitutents. Copolymersencompassing these different types of substituted monomer units areenvisioned by the present invention as well. In both the homopolymersand copolymers of the present invention, between about 0.01% is and 100mole % of the polymer should be provided with Bronsted acid groups.

In a preferred embodiment, the present invention encompasseselectrically neutral polymers given by Formula I or II above. In orderto render the polymers conductive, they must be oxidized so as to removethe M₁ or M₂ moiety and yield a polymer containing a recurringzwitterionic structure according to Ia or IIa. In the preferredembodiment, for example, Ht may be selected from the group consisting ofNH, S, O, Se and Te: M₁ and M₂ each are selected from H, Na, Li or K; Xmay be CO₂, SO₃ or HPO₃ ; and R₁ is a straight chain alkylene or ethergroup (i.e., --(CH₂)_(x) -- or --(CH₂)_(y) O(CH₂)_(z) --, where x and(y+z) are from 1 to about 10), and is a same divalent R₁ group as citedabove when R₂ is present. In a particularly preferred embodiment, Ht isNH or S; M₁ and M₂ are each H, Li or Na; X is CO₂ or SO₃ ; R₁ and R₂ areeach a linear alkyl having from 2 to about.4 carbon atoms; and thesubstituted monomer units of the polymers are either mono- ordi-substituted with R₁ --X--M₁ or R₂ --X--M₂ groups.

In order to "undope" the zwitterionic form of the polymers, an electriccharge may be supplied in the direction contrary to that used in doping(alternatively, a mild reducing agent may be used as discussed below).The M₁ or M₂ moiety is caused to migrate into the polymer and neutralizethe X⁻ counterion. The undoping process is thus as rapid as the dopingprocess.

Scheme I and Scheme II represent the oxidation and reduction of theabove polymers (the mono-substituted embodiment is illustrated), i.e.the transition between the electrically neutral and conductivezwitterionic forms: ##STR3## Where X is CO₂, the above electrochemicalconversion is strongly pH-dependent in the pH range of 1-6 (the PK_(a)for X=CO₂ and M₁ =H in Formula I is about 5). Where X is SO₃, on theother hand, the above electrochemical reaction is pH-independent overthe much larger pH range of about 1-14 (the pK_(a) for X=SO₃ and M₂ =Hin Formula II is about 1). The sulfonic acid derivative is thus chargedat virtually any hydrogen ion concentration, while the carboxylic acidderivative is charged at only lower hydrogen ion concentration. Byvarying the pH of the polymer solution, then, it is easier to controlthe conductivity of the carboxylic acid derivatives than that of thecorresponding sulfonic acid derivatives. The particular Bronsted acidmoiety selected will thus depend on the particular application.

These self-doped polymers have conductivities of at least about 1 S/cm(see Example 14) and typically have chain lengths of about severalhundred monomer units. Typically, chain lengths range from about 100 toabout 500 monomer units; higher molecular weights are preferred.

In the practice of the present invention, a Bronsted acid group isintroduced into a polymer to make it self-doping. The Bronsted acid maybe introduced into a monomer, followed by polymerization orcopolymerization. One may also prepare a polymer or copolymer of theunsubstituted monomers of Formulae I or II and then introduce theBronsted acid into the polymer backbone.

Covalently linking a Bronsted acid to a monomer or polymer is within theskill of the art. See. e.g., J.Am.Chem. Soc. 70:1556 (1948). By way ofillustration, an alkyl group on a monomer or polymer backbone can beconcatenated to an alkyl halide using N-bromo succinamide (NBS) as shownin Scheme III: ##STR4## The halide can then be treated with sodiumcyanide/sodium hydroxide or sodium sulfite followed by hydrolysis togive a carboxylic or sultonic Bronsted acid, respectively, as shown inScheme IV: ##STR5## Another example showing the addition of a Bronstedacid group with an ether linking group is shown in Scheme V: ##STR6##

Syntheses of various monomers useful in the practice of the presentinvention are set forth in Examples 1 through 12, below.

The polymers of the present invention may be synthesized by theelectrochemical methods set forth in, e.g., S. Hotta et al., Synth.Metals 9:381 (1984), or by chemical coupling methods such as thosedescribed in Wudl et al., J. Orq. Chem. 49:3382 (1984). Wudl et al.,Mol. Cryst. Liq. Cryst. 118:199 (1985) and M. Kobayashi et al., Synth.Metals. 9:77 (1984).

When synthesized by electrochemical methods (i.e., anodically), thepolymeric zwitterions are produced directly. With the chemical couplingmethods, the neutral polymers result. The preferred synthetic method iselectrochemical, and is exemplified below by the production of asubstituted polyheterocyclic species.

A solution containing the monomer III ##STR7## with Ht, Y₁, R₁, X and M₁and M as given above, is provided in a suitable solvent such asacetonitrile (particularly suitable for the sulfonic acid derivative,i.e. where X=SO₃) along with an electrolyte such as tetrabutylammoniumperchlorate or tetrabutylammonium fluoroborate. A working electrode ofplatinum, nickel, indium tin oxide (ITO)-coated glass or other suitablematerial is provided, as is a counter electrode (cathode) of platinum oraluminum, preferably platinum. A current of between about 0.5 and 5mA/cm² is applied across the electrodes, and depending on the extent ofpolymerization desired (or the thickness of the polymeric film on asubstrate), the electropolymerization reaction is carried out forbetween a few minutes and a few hours. The temperature of thepolymerization reaction can range from about -30° C. to about 25° C.,but is preferably between about 5° C. and about 25° C.

Reduction of the zwitterionic polymer so produced to the neutral,undoped form may be effected by electrochemical reduction or bytreatment with any mild reducing agent, such as methanol or sodiumiodide in acetone. This process should be allowed to proceed for atleast several hours in order to ensure completion of the reaction.

The sulfonic acid monomer (X=SO₃) is polymerized as the alkyl esterhaving 1 to 2 carbon atoms, such as the methyl ester (see Examples 14and 15). while the carboxylic acid derivative (X=CO₂) may be prepared inits acid form. After polymerization of the sulfonic acid derivative, themethyl group is removed in the treatment with sodium iodide or the like.

The polyanilines represented by Formulae II and IIa may be synthesizedelectrochemically as above or they may be prepared by the reaction of aphenylenediamine with a suitably substituted cyclohexanedione. SchemeVI, below, illustrates this latter synthesis: ##STR8## R₂ and M₂ are asdefined above.

Copolymerization of different types of monomers represented in FormulaeI or II may be effected according to the same procedures outlined above.In a preferred embodiment, the majority of monomers are at leastmono-substituted with an --R₁ --X--M₁ or --R₂ --X--M₂ group asdescribed.

Composites of the polymers of Formulae I and II may be prepared inconjunction with water-soluble polymers such as polyvinyl alcohol (seeExample 17) and the polysaccharides. Because the polymers of the presentinvention may be fairly brittle, preparation of composites usingadditional polymeric materials provides polymers which are more flexibleand less brittle. Films may be cast from aqueous solutions of polymersgiven by Formulae I or II also containing a predetermined amount of oneor more additional water-soluble polymers. Since the key proceduralcriterion in this step is dissolving two or more polymers in water, theonly practical limitation on the additional polymers is that they bewater-soluble.

The polymers of the present invention offer a specific advantage overconventional conducting polymers for use as electrodes inelectrochemical cells. Because the counterions are covalently bound tothe polymer, the cell capacity is not limited by electrolyteconcentration and solubility. This means that in optimized cells, thetotal amount of electrolyte and solvent can be reduced considerably,thus enhancing the energy density of the resulting battery. The facilekinetics of ion transport provided by the novel self-doping mechanismleads to rapid charge and discharge as well as to faster electrochromicswitching. Electrodes fabricated using the polymers of the invention maybe fabricated entirely from these polymers or from conventionalsubstrates coated with these polymers. Conventional substrates mayinclude. for example, indium tin oxide coated glass, platinum, nickel,palladium or any other suitable anode materials. When used as anelectrode, the internal self-doping of the polymer effects thetransition represented by Scheme I.

The self-doped conducting polymers of the invention also offer specificadvantages over conventional conducting polymers for use in a variety ofdevice applications where long term performance requires that the dopantions not be continuously mobile. Examples of such uses includefabrication of Schottky diodes, field effective transistors, etc.Because the dopant ion is covalently bound to the polymer chain inself-doped polymers, the problem of diffusion of the ion (e.g., in thevicinity of a junction or interface) is solved.

EXAMPLES

It is to be understood that while the invention has been described inconjunction with the preferred specific embodiment thereof, that theforegoing description as well as the examples which follow are intendedto illustrate and not limit the scope of the claimed invention. Otheraspects, advantages and modifications within the scope of the inventionwill be apparent to those skilled in the art to which the inventionpertains.

Example 1 2-(3-Thienyl)-Ethyl Methanesulfonate

To a solution of 5.0 g (7.8×10⁻³ mol) of 2-(3-thienyl)-ethanol (AldrichChemical) in 10 ml of dry, freshly distilled pyridine was added 3.62 ml(1.2 equiv.) of methanesulfonyl chloride in 20 ml of pyridine at 5°-10°C. The addition was carried out gradually, over a period of about 15-20min. The reaction mixture was stirred overnight at room temperature andwas quenched by pouring into a separatory funnel containing water andether. The layers were separated and the aqueous layer was extractedthree times with ether. The combined organic extracts were extractedonce with 10% hydrochloric acid, followed by water and drying over Na₂SO₄ Evaporation of the solvent afforded 5.3 g of a light brown oil (65%yield), and tlc (CHCl₃) showed a single spot. Chromatographicpurification on silica gel afforded a light yellow oil. Nmr (CDCl₃. δrel TMS) 2.9s, 3H; 3.1t, 2H; 4.4t, 2H; 7.0-7.4m, 3H. Ir (neat, ν cm⁻¹)3100w, 2930w, 2920w, 1415w, 1355s, 1335s, 1245w, 1173s, 1080w, 1055w,970s, 955s, 903m, 850m, 825w, 795s, 775s, 740w, MS, 206.0.

Example 2 2-(3-Thienyl)-Ethyl Iodide

The above methanesulfonate (5.3 g), 2.6×10⁻² mol) was added to asolution of 7.7g (2 equiv) of NaI in 30 ml of acetone and allowed toreact at room temperature for 24 hr. The CH₃ SO₃ Na which hadprecipitated was separated by filtration. The filtrate was poured intowater, extracted with chloroform, and the organic layer was dried overMgSO₄. Evaporation of the solvent afforded a light brown oil which uponchromatographic purification gave 5.05 g of a light yellow oil (82.5%).Nmr (CDCl₃, δ rel to TMS): 3.2m, 4H; 7.0-7.4m, 3H. Ir (KBr, ν cm⁻¹):3100m, 2960s, 2920s, 2850w, 1760w, 1565w, 1535w, 1450m, 1428s, 1415s,1390w, 1328w, 1305w, 1255s, 1222m, 1170s, 1152m, 1100w, 1080m, 1020w,940m, 900w, 857s, 840s, 810w, 770s, 695s, 633m, MS 238.

Example 3 Sodium-2-(3-Thienyl)-Ethanesulfonate

To a 10 ml aqueous solution of 5.347 g (4.2×10⁻² mol) of Na₂ SO₃ wasadded 5.05 g (0.5 equiv) of the above iodide and the reaction mixturewas heated to 70° C. for 45 hr. The resulting mixture was evaporated todryness followed by washing with chloroform to remove the unreactediodide (0.45 g) and acetone to remove the sodium iodide. The remainingsolid was a mixture of the desired sodium salt contaminated with excesssodium sulfite and was used in subsequent steps without furtherpurification. Nmr (D₂ O, δ rel TMS propanesulfonate): 3.1s, 4H;7.0-7.4m, 3H. Ir (KBr, ν, cm⁻¹, Na₂ SO₃ peaks subtracted) 1272m, 1242s,1210s, 1177s, 1120m, 1056s, 760m, 678w.

Example 4 2-(3-Thienyl)-Ethanesulfonyl Chloride

To a stirred suspension of 2 g of the above mixture of salts prepared inExample 3 was added dropwise 2 ml of distilled thionyl chloride. Themixture was allowed to stir for 30 min. The white solid resulting fromice-water quench was separated by filtration and recrystallized fromchloroform-hexane to afford 800 mg of white crystals, mp 57°-58° C. Nmr(CDCl₃, δ rel TMS) 3.4m, 2H; 3.9m, 2H; 7.0-7.4m, 3H. Ir (KBr, ν, cm⁻¹)3100w, 2980w, 2960w, 2930w, 1455w, 1412w, 1358s, 1278w, 1260w, 1225w,1165s, 1075w, 935w, 865m, 830m, 790s, 770w, 750m, 678s, 625m, El. Anal.Calcd. for C₆ H₇ ClO₂ S₂ : C, 34.20; H, 3.35; Cl, 16.83; S, 30.43.Found: C, 34.38; H, 3.32: Cl, 16.69; S, 30.24.

Example 5 Methyl 2-(3-Thienyl)-Ethanesulfonate (e.g. methylthiophene-3-(2-ethanesulfonate))

To a stirred solution of 105 mg (5×10⁻⁴ mol) of the above acid chloride(prepared in Example 4) in 1.5 ml of freshly distilled (from molecularsieves) methanol was added, at room temperature, 1.74 ml (2 equiv) ofN,N-diisopropylethylamine. The reaction mixture was stirred for 12 hrand then transferred to a separatory funnel containing dilute, aqueousHCl and was extracted with chloroform thrice. After the combined organiclayers were dried with Na₂ SO₄, the solvent was evaporated to afford alight brown oil which was purified by chromatography on silica gel withchloroform as eluent. The resulting colorless solid, obtained in 90%yield had an mp of 27°-28.5° C. Ir (neat film, ν cm⁻¹) 3100w, 2960w,2930w, 1450m, 1415w, 1355s, 1250w, 11656s, 985s, 840w, 820w, 780m, 630w,615w, Uv-vis λmax, MeOH, nm(ε)! 234 (6×10³). Nmr (CDCl₃, δ rel TMS)7.42-7.22q, 1H; 7.18-6.80m, 2H; 3.85s, 3H; 3.6-2.9m, 4H. El. Anal.Calcd. for C₇ H₁₀ O₃ S₂ : C, 40.76; H, 4.89; S, 31.08. Found: C, 40.90;H, 4.84; S, 30.92.

Example 6 Ethyl-2-Carboxyethyl-4-(3-Thienyl)-Butanoate

To a stirred solution of 11.2 g (69.94 mmol) of diethyl malonate in 60ml of freshly distilled DMF, was added 2.85 g (69.94 mmol) of a 60% oildispersion of NaH. After 30 min stirring, 15.86 g (66.61 mmol) of2-(3-thienyl)-ethyl iodide (prepared as described above) in 20 ml of DMFwas added dropwise over 10 min. The reaction mixture was stirred at roomtemperature for one hr and then heated to 140° for four hr. Uponcooling, the reaction was poured into ice-dil. HCl and extracted sixtimes with ether. The combined organic layers were washed with water,dried with Na₂ SO₄ and evaporated to afford a brown oil. Afterchromatography on silica gel (50% hexane in chloroform), a colorless oilwas obtained in 98% yield. El. Anal. Calcd. for C₁₃ H₁₈ O₄ S: C, 57.76;H, 6.71; S, 11.86. Found: C, 57.65; H, 6.76; S, 11.77. Nmr (CDCl₃, δ relTMS) 7.40-7.20t, 1H; 7.10-6.86d, 2H; 4.18q, 4H; 3.33t, 1H; 2.97-1.97m,4H; 1.23t, 6H. Ir (neat film, ν cm⁻¹) 2980w, 1730s, 1450w, 1370w, 775w.

Example 7 2-Carboxy-4-(3-Thienyl)-Butanoic Acid

To a stirred solution of 1.4 g (24.96 mamol) of potassium hydroxide in7.0 ml of 50% ethanol in water, was added the above diestet (765 mg,2.83 mmol) prepared in Example 6. The resulting reaction was allowed tostir at room temperature for two hr, followed by overnight reflux. Theresulting mixture was poured into ice-10% HCl, followed by three etherextractions. The combined organic layer was dired with Na₂ SO₄ andevaporated to afford a white solid in 90% which was recrystallized fromchloroform-hexane to produce colorless needles. Mp, 118°-119° C.; nmr(DMSO/d6, δ rel TMS) 12.60br s, 2H; 7.53-6.80m, 3H; 3.20t, 1H; 2.60t,2H; 1.99q, 2H. Ir (KBr, ν cm⁻¹) 2900w, 1710s, 1410w, 1260w, 925w, 780s,El. Anal. Calcd. for C₉ H₁₀ O₄ S: C, 56.45; H, 5.92; S, 18.83. Found: C,56.39; H, 5.92; S, 18.67.

Example 8 4-(3-Thienyl)-Butyl Methanesulfonate

4-(3-thienyl)-butanoic acid (CA 69:18565x, 72:121265k) was prepared bystandard thermal decarboxylation of the carboxy acid prepared in Example7. This compound was then reduced to give 4-(3-thienyl)-butanol (CA70:68035r. 72: 121265k) also using standard methods.

To a solution of 1.05 g (6.7×10⁻³ mol) of 4-(3-thienyl)-butanol in 25 mlof dry, freshly distilled pyridine was added 0.85 g (1.1 equiv.) ofmethane-sulfonyl chloride at 25° C. The addition was gradual and carriedout over a several minute period. The reaction mixture was stirred for 6hr at room temperature and quenched by pouring into a separtory funnelcontaining water-HCl and ether. The layers were separated and theaqueous layer was extracted once with 10L hydrochloric acid, followed byextraction with water and drying with Na₂ SO₄ Evaporation of the solventafforded 1.51 g of a light brown oil (95% yield), tlc (CHCl₃) showed asingle spot. El. Anal. Calcd. for C₉ H₁₄ O₃ S₂ : C, 46.13; H, 6.02; S,27.36. Found: C, 45.92; H, 5.94: S, 27.15. Nmr (CDCl₃, δ rel TMS)2.0-1.5 brs, 4H; 2.67 brt, 2H; 2.97s, 3H; 4.22t, 2H; 7.07-6.80d, 2H;7.37-7.13, lH.

Example 9 4-(3-Thienyl Butyl Iodide)

The above methanesulfonate (1.51 g. 6.4×10⁻³ mol) prepared in Example 8was added to a solution of 1.93 g (2 equiv.) of NaI in 14 ml of acetoneand allowed to react at room temperature overnight. The reaction mixturewas then heated to reflux for 5 hr. The CH₃ SO₃ Na which hadprecipitated was separated by filtration. The filtrate was poured intowater, extracted with chloroform and the organic layer, was dried withMgSO₄. Evaporation of the solvent afforded a light brown oil which uponchromatographic purification (silica gel, 60% hexane in chloroform) gave1.34 g of a colorless oil (78%). Nmr (CDC₃, δ rel to TMS) 1.53-2.20m,4H; 2.64t, 2H; 3.17t, 2H; 6.83-7.10d, 2H; 7.13-7.37t, 1H. Ir (KBr, νcm⁻¹) 2960s, 2905s, 2840s, 1760w, 1565w, 1535w, 1450s. 1428s, 1415s,1190s, 750s, 695m, 633m. MS 266.0. El. Anal. Calcd. for C₈ H₁₁ IS: C,36.10; H, 4.17; I, 47.68; S, 12.05. Found: C, 37.68; H, 4.35; I, 45.24;S, 12.00

Example 10 Sodium-4-(3-Thienyl)-Butanesulfonate

To a 2 ml aqueous solution of 1.271 g (1×10⁻² mol) of Na₂ SO₃ was added1.34 g (0.5 equiv) of the above iodide prepared in Example 9. Thereaction mixture was heated to reflux for 18 hr. The resulting mixturewas evaporated to dryness, followed by washing with chloroform to removethe unreacted iodide and with acetone to remove the sodium iodide. Theremaining solid was a mixture of the desired sodium salt contaminatedwith excess sodium sulfite and was used in subsequent steps withoutfurther purification. Nmr (D₂ O, δ rel TMS propane-sufonate) 1.53-1.97m,4H; 2.47-3.13m, 4H; 6.97-7.20d, 2H; 7.30-7.50q, 1H. Ir (KBr, ν cm⁻¹, Na₂SO₃ peaks subtracted) 2905w, 1280m, 1210s, 1180s, 1242m, 1210s, 1180s,1130s, 1060s, 970s, 7700s, 690w, 630s, 605s.

Example 11 4-(3-Thienyl)-Butanesulfonyl Chloride

To a stirred suspension of 1.00 g of the above mixture of salts (fromExample 10) in 10 ml of freshly distilled DMF was added dropwise 1.43 gof distilled thionyl chloride. The mixture was allowed to stir for 3 hr.The slighly yellow oil resulting from ice-water quench was isolated bytwice extracting with ether, followed by drying of the organic layerwith Na₂ SO₄ to yield 566 mg of a slightly yellow oil which crystallizedslowly (mp 26°-27°) after chromatography (silica gel. chloroform). Nmr(CDCl₃, δ rel TMS) 1.45-2.38m, 4H; 2.72t, 2H; 3.65t, 2H; 6.78-7.12d, 2H;7.18-7.42, 1H. Ir (neat film, ν cm⁻¹) 3120w, 2920s, 2870m, 1465m, 1370s,1278w, 1260w, 1160s, 1075w, 935w, 850w, 830m, 7765s, 680m, 625w, 585s,535s, 510s, El. Anal. Calcd. for C₈ H₁₁ ClO₂ S₂ : C, 40.25; H, 4.64; Cl,14.85; S, 26.86. Found: C, 40.23; H, 4.69; Cl, 14.94; S, 26.68.

Example 12 Methyl 4-(3-Thienyl)-Butanesulfonate (e.g. methylthiophene-3-(4-butanesulfonate))

To a stirred solution of 362 mg (1.5×10⁻¹ mol) of the above acidchloride prepared in Example 11 in 6 ml of freshly distilled (frommolecular sieves) methanol was added, at room temperature, 392 mg (2equiv) of N,N-diisopropylethylamine. The reaction mixture was stirredfor 2 hr and then transferred to a separatory funnel containing dilute,aqueous HCl and was extracted with chloroform thrice. After the combinedorganic layers were dried with Na₂ SO₄, the solvent was evaporated toafford a light brown oil which was purified by chromatography on silicagel with 40% hexane in chloroform as eluent. The resulting colorlessoil, obtained in 84% yield had the following properties: El. Anal.Calcd. for C₉ H₁₄ S₂ O₃ : C, 46.13; H, 6.02; S, 27.36. Found: C, 45.97;H, 5.98; S, 27.28. Ir (neat film, ν cm ) 3100w, 2970m, 2860w, 1460m,1410w, 1350s, 1250w, 1160s, 982s, 830m, 800m, 770s, 710w, 690w, 630w,613w, 570m, Uv-vis λmax, MeOH, nm (ε)! 220 (6.6×10³). Nmr (CDCl₃, δ relto TMS) 7.33-7.13 (t, 1H), 7.03-6.77 (d, 2H), 3.83 (s, 3H), 3.09 (t,2H), 2.67 (t,2 H), 2.2-1.5 (m, 4H).

Example 13

Polymerization of Thiophene-3-Acetic Acid ##STR9##

Thiophene-3-acetic acid (Formula IV) was polymerized at room temperatureby the electrochemical polymerization method of S. Hotta et al., Synth.Metals, supra, using acetonitrile as the solvent and LiClO₄ as theelectrolyte. Blue-black films were produced, indicating formation of thezwitterionic polymer of Formula Ia, (Y₁ =H, R₁ =--CH₂ --, Ht=S, andX=CO₂. The polymer films were electrochemically cycled and observed toundergo a color change from blue-black to yellowish brown, indicatingreduction of the zwitterionic form of the polymer to the neutral formrepresented by Formula I. The infrared spectrum was in agreement withthe proposed structure.

Example 14 Poly(Thiophene-3-(2-Ethanesulfonic Acid Sodium Salt))##STR10##

Methyl thiophene-3-(2-ethanesulfonate) (Formula V) was prepared asabove. Polymerization of the above monomer was carried out as in Example13, except that the polymerization temperature was maintained at -27° C.The resultant polymer ("methyl P3-ETS", Formula VI) was then treatedwith sodium iodide in acetone to remove the methyl group from thesulfonic acid functionality and produce, in quantitative yield (˜98%),the corresponding sodium salt of the polymer, i.e. ofpoly(thiophene-3-(2-ethanesulfonic acid)) ("P3-ETSNa") as shown inFormula VII. The polymeric methyl ester and the polymeric sodium saltwere characterized by infrared and ultraviolet spectroscopy as well asby elemental analysis (see FIGS. 1 and 2). The sodium salt was found tobe soluble in all proportions in water, enabling the casting of filmsfrom aqueous solution.

Electrochemical cells were constructed in glass to demonstrateelectrochemical doping and charge storage via in situoptoelectrochemical spectroscopy. The cells included a film of the abovepolymer on ITO-coated glass (which served as the anode), a platinumcounterelectrode (cathode) and a silver/silver chloride referenceelectrode with tetrabutylammonium perchlorate as electrolyte. FIG. 5depicts a series of vis-near ir spectra of the P3-ETSNa taken with thecell charged to a series of successively higher open circuit voltages.The results were typical of conducting polymers in that the π-π*transition was depleted with a concomitant shift of oscillator strengthinto two characteristic infrared bands. The results of FIG. 5demonstrate both reversible charge storage and electrochromism.

The electrical conductivity was measured with the standard 4-probetechniques using a film of the polymer cast from water onto a glasssubstrate onto which gold contacts had been previously deposited. uponexposure to bromine vapor, the electrical conductivity of P3-ETSNa roseto ˜1 S/cm.

Example 15 Poly(Thiophene-3-(4-Butanesulfonic Acid Sodium Salt))##STR11##

Methyl thiophene-3-(4-butanesulfonate) (Formula VIII) was prepared asabove. Polymerization was carried out under conditions identical tothose set forth in Examples 13 and 14 above. The resultant polymer(designated "methyl P3-BTS", Formula IX) was treated with sodium iodidein acetone to produce, in quantitative yield, the sodium salt ofpoly(thiophene-3-(4-butanesulfonic acid)) ("P3-BTSNa", Formula X). Thepolymeric methyl ester (Formula IX) and the corresponding sodium salt(Formula X) were characterized spectroscopically (ir, uv-vis) and byelemental analysis. The sodium salt was discovered to be soluble in allproportions in water, enabling the casting of films from aqueoussolution.

Electrochemical cells were constructed as in Example 14 in order todemonstrate electrochemical doping and charge storage via in situoptoelectrochemical spectroscopy. FIGS. 6 and 7 depict a series ofvis-near ir spectra of the P3-BTSNa and methyl P3-BTS respectively.taken with the cells charged to successively higher open circuitvoltages. As in Example 14, the results were found to be typical ofconducting polymers in that the π-π* transition was depleted with aconcomitant shift of oscillator strength into two characteristicinfrared bands. As in Example 14, the results of FIGS. 6 and 7demonstrate both reversible charge storage and electrochromism.

Example 16 Polymerization and Analysis ofPoly(Thiophene-3-(2-Ethanesulfonic Acid))

The polymeric sodium salt of thiophene-3-(2-ethanesulfonic acid) (Ht=S,Y₁ =H, X=SO₃, M=H) was prepared as outlined above, dissolved in waterand subjected to ion exchange chromatography on the acid form of acation exchange resin. The results of atomic absorption analysis of thedark red-brown effluent indicated complete replacement of sodium byhydrogen. FIG. 8 shows the results of cyclic voltammetry carried out onfilms of the polymer ("P3-ETSH"/ITO glass working electrode, platinumcounterelectrode, and a silver/silver chloride reference electrode inacetonitrile with fluoroboric acid-trifluoroacetic acid as electrolyte).The figure indicates that P3-ETSH is an electrochemically robust polymerwhen cycled between +0.1 and +1.2 V versus silver/silver chloride in astrongly acidic medium. There are two closely spaced oxidation waves,the first of which corresponds to a change in color from orange togreen. The polymer could be cycled and corresponding color changesobserved without noticeable change in stability at 100 mV/sec.

Electrochemical cells were constructed in glass to demonstrateelectrochemical doping and charge storage via in situoptoelectrochemical spectroscopy, substantially as in the previous twoExamples. The cells consisted of a film of the polymer on ITO glass(anode), platinum counterelectrode (cathode) and a silver/silverchloride reference electrode in acetonitrile with fluoroboricacid-trifluoroacetic acid as electrolyte.

FIG. 9 depicts a series of vis-near ir spectra of the P3-ETSH taken withthe cell charged to a series, of successively higher open circuitvoltages. In this case, the polymer was observed to spontaneously dopein the strongly acidic electrolyte solution. The results of FIG. 9demonstrate both reversible charge storage and electrochromism. Controlof the self-doping level for brief periods of time was achieved byimposing a voltage lower than the equilibrium circuit voltage.

Example 17 Preparation of Polymer Composite

Poly(thiophene-3-(2-ethanesulfonic acid)) (Formula I, Ht=S, Y₁ =H, --CH₂CH₂ --, X=SO₃, N₁ =H, "P3-ETSH") as prepared in Example 4 was used toprepare a composite as follows. The compound was admixed with a solutionof polyvinyl alcohol in water, and films of the neutral polymer werecast. Free standing deep orange films (indicating charge neutrality, asopposed to the blue-black zwitterionic polymers) cast from the preparedsolution had excellent mechanical properties (soft, smooth and flexible)and could be chemically doped and undoped by compensation. This methodof making conducting polymer composites is broadly applicable to the useof any water-soluble polymer in conjunction with P3-ETSH or P3-BTSH.

Example 18 Preparation of Polymer of2,5-Diethoxycarbonyl-1,4-Cyclohexanedione and p-Phenylenediamine

To a suspension of 8.51 g (33.21 mmole) of2,5-dicarboxyethyl-1,4-cyclohexanedione in 380 ml of freshly distilledbutanol was added 3.59 g of p-phenylenediamine in 20 ml of butanol,followed by 40 ml of glacial acetic acid. The resulting mixture washeated to reflux for a period of 36 hrs, then it was exposed to oxygenby refluxing over a period of twelve hours, was hot filtered, the solidwas washed with ether and extracted in a Soxhlet extractor with thefollowing solvents: chloroform (6 days), chlorobenzene (5 days), andether (4 days). This treatment afforded a dark solid (8.42 g). Elementalanalysis calcd. for C₁₈ H₁₈ N₂ O₄ : C, 65.84; H, 6.14; N, 8.53. Found:C, 65.55; H, 6.21; N, 8.70. Ir (KBr, ν cm-1): 3350w, 3240w, 2980m,2900w, 1650s, 1600s, 1510s, 1440m, 1400w, 1220s, 1090w, 1065s, 820w,770m, 600w, 495w.

Example 19 Polyaniline Dicarboxylic Acid

The above polymer diester is suspended in DMF and treated with asolution of 50% (w/w) sodium hydroxide. The reaction mixture is thenheated to 100° C. for 48 hr under strictly anaerobic conditions toexclude oxygen. Upon cooling the mixture, it is poured into ice/HCl andfiltered. The infrared spectrum of the product should show the followingcharacteristic absorption peaks: 3100-2900br, 1600s, 1500s, 1210s.

We claim:
 1. A method of making a self-doped zwitterionic conductingpolymer having along its backbone a π-electron conjugated system, whichmethod is selected from the following methods (A) or (B):wherein method(A) which comprises:(i) providing a polymer having along its backbone aπ-electron conjugated system which comprises a plurality of recurringmonomer units, between about 0.01 and 100 mole % of said units havingthe structure (I): ##STR12## wherein Ht is a heterogroup selected fromNH or S; Y₁ is selected from the group consisting of hydrogen and--R--X--M, whereinR is a linear or branched alkylene or alkylene etherhaving between 1 and about 10 carbon atoms; X is a Bronsted acid anionselected from CO₂ or SO₃ ; and M is a positive monovalent counterionexcept H⁺ ; and (ii) converting at least one --R--X--M group to a--R--X--H group by adding acid, thereby rendering said polymerself-doped, with the proviso that external dopant is not needed and isnot present; or method (B) which comprises;(a) providing at least onemonomer having the structure: ##STR13## wherein Ht is a heterogroupselected from NH or S; Y₁ is selected from the group consisting ofhydrogen and --R--X--M, whereinR is a linear or branched alkylene oralkylene ether having between 1 and about 10 carbon atoms; --X--M is aBronsted acid alkyl ester group, or X is a Bronsted acid anion selectedfrom CO₂ or SO₃ and then M is a positive monovalent counterion, and (b)polymerizing said monomers, and if M is not H⁺, then (c) converting atleast one --R--X--M group to a R--X--H group by adding acid, therebyrendering said polymer self-doped, with the proviso that external dopantis not needed and is not present.
 2. The method of claim 1, wherein themethod (B) comprises the steps of:providing an electrolyte solutioncomprising said monomer, immersing in said electrolyte solution, aworking electrode and a counter electrode; and applying a voltage acrosssaid working electrode and said counter electrode, wherebypolymerization of said monomer at said working electrode is effected toproduce a polymer having along its backbone a π-electron conjugatedsystem which comprises a plurality of recurring monomer units, betweenabout 0.01 and 100 mole % of said units having the structure: ##STR14##wherein Ht is a heterogroup selected from NH or S; Y₁ is selected fromthe group consisting of hydrogen and --R--X--M, wherein R is a linear orbranched alkylene or alkylene ether having between 1 and about 10 carbonatoms; --X--M is a Bronsted acid or alkyl ester group, or X is aBronsted acid anion selected from COO or SO₃ and then M is a positivemonovalent counterion alkyl, andif M is not H⁺, then further comprisingthe step of converting at least one --R--X--M group to a R--X--H groupby adding acid, thereby rendering said polymer self-doped.
 3. The methodof claim 1 wherein R is linear alkylene.
 4. The method of claim 1wherein R is branched alkylene.
 5. The method of claim 1 wherein:M inmethod (A) is selected from the group consisting of Li⁺, Na⁺ and K⁺ ;and M in method (B) is selected from the group consisting of H⁺, Li⁺,Na⁺, K⁺, methyl and ethyl.
 6. The method of claim 2 wherein R isbranched alkylene ether.
 7. The method of claim 2 wherein and R islinear alkylene ether.
 8. The method of claim 2 wherein M in method (A)is selected from the group consisting of Li⁺, Na⁺ and K⁺ ; and M inmethod (B) is selected from the group consisting of H⁺, Li⁺, Na⁺, K⁺,methyl and ethyl.
 9. The method of claim 3 wherein R is branchedalkylene ether.
 10. The method of claim 9 wherein Ht is NH.
 11. Themethod of claim 1 wherein Ht is S.
 12. The method of claim 1 wherein Xis CO₂.
 13. The method of claim 10 wherein X is SO₃.
 14. The method ofclaim 11 wherein X is CO₂.
 15. The method of claim 9 wherein X is SO₃.16. The method of claim 10 wherein X is SO₃.
 17. The method of claim 11wherein X is SO₃.
 18. The method of claim 5 wherein M in method (A) isNa⁺ or K⁺.
 19. The method of claim 5 wherein M in method (B) is H⁺, Na⁺or K⁺.
 20. The method of claim 5 wherein M in method (A) is Na⁺ or K⁺,and Ht is S.
 21. The method of claim 5 wherein M in method (B) is H⁺,Na⁺ or K⁺, and t is NH or S.
 22. The method of claim 1, wherein saidmonomer is selected from the group consisting of thiophene-3-aceticacid, methyl thiophene-3-(2-ethanesulfonate), and methylthiophene-3-(4-butanesulfonate).